Drop windows of this type are present in the doors of modern motor vehicles and therefore are generally well known. They are used in coupes and cabriolets which have a frameless door. On conventional vehicles, the necessary tension is achieved by slanting the guide rails transversely to the direction of travel. When the window pane is raised, immediately before reaching its end position it undergoes a pivoting motion through which it is pressed against the pane seal. However, prior windows do not have means for adjusting the position of the window pane in the closed state. Therefore, the guide rails of the drop window must be very precisely aligned in order to avoid differences in alignment between the closed window pane and the outer skin of the vehicle.
In motor vehicles known in practice, it is known that adjusting means are provided on both guide rails of the window pane inside the door structure which make it possible to swivel the lower ends of the guide rails transversely to the plane of the door. The disadvantage here, however, is that both guide rails must always be uniformly adjusted so that they remain aligned parallel with one another. If only one guide rail were adjusted, the window pane would be twisted such that the forces necessary for its adjustment would have to be increased considerably over its entire stroke distance. In many vehicles, an adjustment of the two guide rails is impossible because the front guide rail is raised up out of the door opening nearly to the roof and is firmly connected to a window frame. Add to this the fact that in the lower region of modern motor vehicles, usually a brace, as a side collision protection, is provided which occupies the space for the adjusting means.